I watched the replay several times over at NFL.com.
#1, it's not clear that Joyner could have avoided contact - it looked like he went low right about the same time Bridgewater began his slide. As close in time as those two events occur, it's probably beyond the ability of human reaction time to have avoided contact. As long as Bridgewater was running upright, Joyner has every right to go into try to tackle him. If Bridgewater starts to slide at just about the same time Joyner commits to making a tackle, that's just unfortunate timing, not dirty play.
#2 In contrast to what the game announcers said (and others have written), Joyner most decidedly did not use his forearm on Bridgewater. As you watch the play unfold, once Joyner realizes that Bridgewater is sliding, he actually pulls his arm into his own body. It was the side of Joyner's upper arm that actually makes contact with Bridgewater's helmet. If you are trying to execute a dirty hit, that certainly seems like an unusual part of the arm to do it with.
So looking at the replay, I have a hard time seeing where Joyner was doing anything other than playing hard nosed football. Zimmerman is supposed to be an old school coach, he should quit whining, injuries like that happen. Unfortunate, but not intentional. Just bad timing.
Two other points, one somewhat related to the play, the other one not:
#3 Ironically, only a few plays earlier, TruJo go flagged for defensive holding on an atrociously bad call. Had he not been, it would have set up 3rd and 16 much deeper in their own territory. The likelihood of Bridgewater scrambling such a play would have been much less, and it's probable the way the defense was playing that they would have gotten the stop. Instead, their drive was extended by a penalty that should have never been called, and Bridgewater ended up getting KO'd a few plays later (FYI, it was 2nd and 1 on the play he was injured).
#4 With respect to his thinly veiled jabs at Fisher and Williams, at least those guys never referred to a child-beater as a role model. Can't say the same for Zimmerman.